At its inception radio telephony was designed, and used for, voice communications. As the consumer electronics industry continued to mature, and the capabilities of processors increased, more devices became available for use that allowed the wireless transfer of data between devices. Also more applications became available that operated based on such transferred data. Of particular note are the Internet and local area networks (LANs). These two innovations allowed multiple users and multiple devices to communicate and exchange data between different devices and device types. With the advent of these devices and capabilities, users (both business and residential) found an increasing need to transmit data, as well as voice, from mobile locations.
The infrastructure and networks which support this voice and data transfer have likewise evolved. Limited data applications, such as text messaging, were introduced into the so-called “2G” systems, such as the Global System for Mobile (GSM) communications. Packet data over radio communication systems were implemented in GSM with the addition of the General Packet Radio Services (GPRS). 3G systems introduced by Universal Terrestrial Radio Access (UTRA) standards made applications like surfing the web more easily accessible to millions of users (and with more tolerable delay). Thus, numerous radio access technologies (RATs), such as e.g. Wideband Code Division Multiple Access (WCDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Time Division Multiple Access (TDMA), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), and others, can be found in use today in wireless systems such as e.g. GSM, Universal Mobile Telecommunication System (UMTS), UMTS-LTE, Wireless Local Area Network (WLAN), Wi-Fi, etc.
Even as new network designs are rolled out by network manufacturers, future systems which provide greater data throughputs to end user devices are under discussion and development. For example, the so-called 3GPP Long Term Evolution (LTE) standardization project is intended to provide a technical basis for radio communications in the years to come. This evolution of network designs has resulted in various network operators deploying their networks in various frequency bands with different RATs in various geographical areas. As a result of this, a user equipment (UE) which supports several frequency bands and/or several different RATs will need to be able to, among other things, search for cells and service in a correct frequency band and/or RAT.
The rapid development of new standards for mobile telephony and other communication technologies and the even more rapid addition of new features to the existing standards drive higher design costs for devices which use the currently existing architectures. For example, devices which enable access to a particular RAT or RATs typically have a software (SW) architecture that is tailored to that RAT(s) and its current features. When a new RAT or feature is added to a multi-RAT UE device architecture, not only the new RAT/feature has to be implemented in the architecture but also the legacy implementations have to be adapted, which process typically seriously affects the software implementation and adds significantly to the devices' costs.
This methodology for introducing a new RAT, or a new functionality to an existing RAT, makes the SW architecture of UEs complex and it becomes difficult to make the modifications that are necessary to adapt to such changes. Additionally, development is often performed at different geographical sites, sometimes located in different continents, causing the integration to be even more complicated and costly.
As described above, today's UEs can be capable of communicating with multiple wireless networks. In order to support mobility among other different networks, the UEs should be able to perform cell-reselection/handover related measurements on neighbor cells. A UE typically communicates with a serving cell in only one wireless network at a given moment (which is known as the active RAT) but in the background, the UE can periodically make measurements for cells in other wireless networks. The cell measurements may include, for example, measurements for received signal strength, timing, frequency and cell identification.
If the active RAT is a UMTS Frequency Division Duplexing (FDD) system, the UE uses continuous transmission and reception operation in the dedicated mode, and therefore measurement gaps need to be created artificially. On command from the UTRAN, the UE monitors cells on other FDD frequencies and on other modes and RATs that are supported by the UE, e.g., LTE, TDD, and GSM. The compressed mode is used in the CELL_DCH state only. To allow the UE to perform measurements, the UTRAN commands the UE to enter a compressed mode, depending on the UE capabilities. In the UE idle mode, URA_PCH and CELL_PCH states, the compressed mode is not needed for inter-frequency and inter-RAT (I-RAT) measurement because there is no continuous reception of any channel. The paging channel (PICH/PCH) is based on discontinuous reception (DRX) and the broadcast channel (BCH) of the serving cell is only required when system information changes.
In the CELL_FACH state, there are forward access channel (FACH) measurement occasions that are used to generate the equivalent connection management (CM) gap and can reasonably be used for inter-frequency and I-RAT measurements. It is to be understood that these FACH measurement occasions are increments of frames rather than timeslots. The UE attempts to detect, synchronize and monitor intra-frequency, inter-frequency and I-RAT cells indicated in the measurement control system information of the serving cell. UE measurement activity is also controlled by measurement rules defined in 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 25.304.
If the active RAT is an LTE FDD system, the compressed mode is no longer applicable so a scheduled gap measurement is proposed. An Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) needs to provide a period in which no downlink data will be scheduled for the UE. In the active state, the eNB (e-nodeB) provides measurement gaps in the scheduling of the UE, where no downlink or uplink scheduling occurs. Ultimately the network makes the decision, but the gap provides the UE sufficient time to change frequency, make a measurement change and switch back to the active channel. This can normally occur in a few Transmission Time Intervals (TTIs). This has to be coordinated with the DRX, which also causes the system to shut off the radio for periods of time to save power. Also, in connected mode LTE, the gaps are not uniformly distributed and there is a DRX.
In the UE, if one of the supported RATs is GSM and an active RAT is LTE or UMTS, then the UE measures the signal level of the GSM Broadcast Control Channel (BCCH) carrier of each GSM neighbor cell indicated in the measurement control system information of the serving cell at least every Tmeasure GSM, according to the measurement rules defined in 3GPP TS 36.133 (for LTE) and 3GPP TS 25.133 (for UMTS). According to these measurement rules, the UE shall attempt to verify the Base Station Identity Code (BSIC), which is a six bit code and each BTS in GSM has a BSIC which identifies it, at least every Treconfirm.gsm (in LTE) or Nre-confirm—abort (in GSM) for each of the four strongest GSM BCCH carriers. The UE then ranks the verified GSM BCCH cells according to the cell reselection criteria. If a change of BSIC is detected for one GSM cell then that GSM BCCH carrier shall be treated as a new GSM neighbor cell. If the UE detects a BSIC, which is not indicated in the measurement control system information, the UE shall not consider that GSM BCCH carrier in cell reselection. The UE also shall not consider the GSM BCCH carrier in cell reselection, if the UE cannot demodulate the BSIC of that GSM BCCH carrier.
If the active RAT is GSM, after the UE selects a particular cell/BCCH carrier to listen to when the UE is in idle mode, the UE shall continue to monitor all BCCH carriers as indicated in the base station allocation (BA) list (see, e.g., 3GPP TS 45.008 section 6.6.1). The UE shall monitor first the RSSI of the non-serving carriers, up to 32 carriers. Then, if a new carrier is found, whose signal strength is greater than the defined threshold, the UE will schedule Frequency Correction Channel (FCCH) detection on that carrier. If FCCH is detected, SCH detection will then be scheduled by the UE for that carrier after getting the rough timing information about in which TDMA frame, the SCH on that carrier will be appearing. If the SCH is decoded properly, then the SCH decoded data will convey the Reduced Frame Number (RFN) which is 19 bits and the BSIC which includes a three bit base station identity code BCC and a three bit network identity code (NCC). The UE then checks the validity of the BSIC and if the BSIC is new, e.g., the cell is new and allowed, the cell is added in the cell list if it was not added earlier. Once a new cell is found and added in the cell list, the UE tries to monitor that cell on a regular basis to re-confirm that it is actually monitoring the same cell. This process is known as BSIC reconfirmation. Also when in the dedicated mode, the UE performs this BSIC reconfirmation.
According to 3GPPP TS 45.008, the UE shall attempt to check the BSIC for each of the six strongest non-serving cell BCCH carriers at least every 30 seconds to confirm that the UE is monitoring the same cell and that it is essential for the UE to identify which surrounding Base Station Subsystem (BSS) is being measured in order to ensure reliable handover. Thus, it is necessary for the UE to synchronize to and demodulate surrounding BCCH carriers as well as identify the BSIC. The UE shall attempt to demodulate the SCH on the BCCH carrier of as many surrounding cells as possible and to decode the BSIC as often as possible, at least once every 30 seconds. A list containing BSIC and timing information for these strongest carriers at the accuracy required for access to a cell (see 3GPP TS 45.010) including the absolute times derived from the parameters T1, T2 and T3 shall be kept by the UE. This information may be used to schedule the decoding of the BSIC and is used when re-selecting a new cell in order to keep the switching time at a minimum.
It is desirable that the cell measurements and cell reconfirmation should be completed as soon as possible for various reasons, such as, faster monitoring, more quickly going into a sleep mode for power saving, etc. As described above, the BSIC identification should happen very frequently in a UE and occurs in the idle mode as well as in the dedicated mode or packet transfer mode.
When the UE is operating in LTE, WCDMA or GSM as the active RAT and the UE is in the idle mode condition, as shown in FIG. 1, the UE periodically wakes up according to the DRX period of that mode to perform paging reception, measurements and cell re-confirmations related to activities in the Active Period 2. As the UE frequency needs to be stable, before the paging reception and other activities, the UE ideally wakes up a bit early, e.g., approximately five ms before the Active Period 2 to get ready for AFC, HW configuration, stabilization etc., which is known as the Pre-wake Up period 4.
For the interested reader, the requirements for GSM measurements are listed in 3GPP TS 45.008 (GSM), 3GPP TS 25.133 (WCDMA) and 3GPP TS 36.133. GSM measurements can be divided into three different types: (1) GSM carrier RSSI measurement, (2) GSM carrier BSIC search, i.e., the initial BSIC identification, and (3) periodic BSIC re-confirmation in which after the initial synchronization has been found, this process is periodically confirming that by checking the cell identity repeatedly.
Returning to the present scenario, the RSSI measurement can be performed with the idle mode Active Period 2 so that the UE can complete the BCCH carriers signal strength measurement in this wake up period. Also, it is desirable to complete the other periodic task of BSIC reconfirmation in the same Active Period 2. This allows for the UE to complete all of the activities during the same wakeup period and thus to quickly go to sleep again and need not have to wake up again after some time to receive the SCH burst for cell re-confirmation. However, the main bottleneck for this procedure is to complete the cell reconfirmation as the UE has to read the SCH burst data of every neighbor cell according to the BA list or cell list for cell reconfirmation.
Now, as shown in FIG. 2, the SCH uses a Synchronization Burst (SB) and appears in the 51 multi-frame structure 6 of that neighbor cell's BCCH frequency. In FIG. 2, for the GSM network 51 multi-frame structure, F is the FCCH, S is the SCH, B is the BCCH, P s the PCCH or CCCH channel and I is for an idle frame. These channels appear in a time multiplexed manner in the same frequency and time slot in a repeating sequence as shown.
According to the presently existing implementation for GSM neighbor cell reconfirmation purpose, the UE has to receive the neighbor cell's SCH, which contain the SB burst, and then demodulate and decode it to get the BSIC. The UE checks the validity of the BSIC and, if the BSIC is new, e.g., the cell is new, and if that cell is allowed then the cell is added to the cell list unless it was already on the cell list. Otherwise, if the BSIC matches the BSIC previously stored for that cell then the UE reconfirms the synchronization with that neighbor cell's Base Station.
However, GSM and WCDMA are asynchronous systems. The cells in each network operate asynchronously of one another. This asynchronous operation at the cell (GSM cells) and network (RAT) level complicates the cell measurement and confirmation. Because these serving and neighbor cells are not perfectly time aligned, each neighbor cell's 51 multi-frame structure is not time aligned. Therefore, the UE needs to keep track of the time offsets. Typically, the UE maintains a cell timing offset database for monitoring of all the neighbor cells.
However, as described above, there is no guarantee that all of the neighbor cells' SCH timeslots will fall within the Active Period 2, e.g., or guarantee that the paging activity period and that all neighbor cells' SCHs will coincide all of the time. This causes a major difficulty in the current, conventional I-RAT implementation.
A similar problem also exists in an active RAT's dedicated mode as well since the measurement time available is very short. For example, in WCDMA dedicated mode, creating suitable gap patterns using compressed mode is not easy and also involves sacrifice to throughput handling. In the LTE active RAT case, the gaps are not regular since LTE has DRX in the connected mode. So, making sure that all of the neighbor cells' SCHs will fall inside the provided measurement time gap period is very difficult to achieve and to confirm the cells BSICs is practically not possible to always achieve. For example, FIG. 3 shows a dedicated mode scenario including measurement time gap 8 which gap 8 does not coincide with either SCH timeslot(s) 7, 9 of its GSM neighbor cells #1 and #2.
Accordingly, it would be desirable to provide methods and systems which improves cell reconfirmation.